Content deleted Content added
Deltahedron (talk | contribs) →Related concepts: Berstel et al (2010) |
Deltahedron (talk | contribs) not always possible, but it might be |
||
Line 3:
Prefix codes are also known as '''prefix-free codes''', '''prefix condition codes''' and '''instantaneous codes'''. Although [[Huffman coding]] is just one of many algorithms for deriving prefix codes, prefix codes are also widely referred to as "Huffman codes", even when the code was not produced by a Huffman algorithm. The term '''comma-free code''' is sometimes also applied as a synonym for prefix-free codes<ref>US [[Federal Standard 1037C]]</ref><ref>{{citation|title=ATIS Telecom Glossary 2007|url=http://www.atis.org/glossary/definition.aspx?id=6416|accessdate=December 4, 2010}}</ref> but in most mathematical books and articles (e. g.<ref>{{citation|last1=Berstel|first1=Jean|last2=Perrin|first2=Dominique|title=Theory of Codes|publisher=Academic Press|year=1985}}</ref><ref>{{citation|doi=10.4153/CJM-1958-023-9|last1=Golomb|first1=S. W.|author1-link=Solomon W. Golomb|last2=Gordon|first2=Basil|author2-link=Basil Gordon|last3=Welch|first3=L. R.|title=Comma-Free Codes|journal=Canadian Journal of Mathematics|volume=10|issue=2|pages=202–209|year=1958|url=http://books.google.com/books?id=oRgtS14oa-sC&pg=PA202}}</ref>) it is used to mean [[self-synchronizing code]]s, a subclass of prefix codes.
Using prefix codes, a message can be transmitted as a sequence of concatenated code words, without any [[out-of-band]] markers to [[framing (telecommunication)|frame]]{{Disambiguation needed|date=February 2012}} the words in the message. The recipient can decode the message unambiguously, by repeatedly finding and removing prefixes that form valid code words. This is not always possible with codes that lack the prefix property, for example {0, 1, 10, 11}: a receiver reading a "1" at the start of a code word would not know whether that was the complete code word "1", or merely the prefix of the code word "10" or "11".
The variable-length [[Huffman coding|Huffman codes]], [[country calling codes]], the country and publisher parts of [[ISBN]]s, the Secondary Synchronization Codes used in the [[UMTS]] [[W-CDMA]] 3G Wireless Standard, and the [[instruction set]]s (machine language) of most computer microarchitectures are prefix codes.
| |||